Heat illness, or heat exhaustion, is a common problem affecting firefighters, road and building contruction workers, and other personnel in situations demanding physical exertion, the use of protective garments, or work in harsh environments. In these and other situations, body heat, or metabolic heat, combines with radiant heat from the environment to elevate the person's body temperature. The body also gains heat by convection when the ambient air temperature rises above normal body temperature (98.6 degrees F.). The body attempts to control its temperature by raising and lowering the heart rate (raising and lowering blood pressure), sending blood to the surface of the skin, and through perspiration. As the perspiration evaporates, heat is drawn from the body. However, in situations where protective garments such as firefighting suits or protective jackets, boots, gloves, and so on are needed, the body's natural evaporative cooling process becomes overburdened.
Studies conducted on firefighters have shown that fire suppression activities produce over 400 kilocalories of heat per hour and that another 180 kilocalories of per hour can be attributed to radiant heat (heat from the fire). Evaporation of over one quart of perspiration is needed to remove 580 kilocalories of heat. Therefore, a firefighter needs to evaporate over one quart of perspiration during each hour of work in order to maintain a safe body temperature.
Heat illness occurs as the body loses its ability to regulate temperature and affects not only the person's welfare but also cognitive abilities. Notwithstanding the increased potential for dangerous accidents due to heat illness symptoms, left untreated, heat illness can rapidly lead to progressively worse conditions or even death.
Heat illness generally has three stages: heat stress, heat exhaustion, and heat stroke. These stages are often difficult to distinguish, therefore experts recommend treating for the worst case when there is any doubt. Symptoms of heat stress include cool or moist skin, weakness, dizziness, and nausea. Treatment for heat stress includes moving the victim to an area of shade, loosening the victim's clothing, and giving the victim water. The symptoms of heat exhaustion include a weak pulse (low blood pressure), shallow breathing (breathing rate increasing), clammy skin (perspiring), a pale face, a loss of appetite, and possible confusion and irritability. And treatment for heat exhaustion includes all the steps for heat stress plus sponging the victim with water, fanning to increase evaporation, and seeking medical attention. Finally, the symptoms of heat stroke include a rapid pulse, hot or dry skin (no perspiration), a high body temperature (over 105 degrees F.), mental confusion, and a loss of consciousness. The treatment for heat stroke includes all the steps for heat exhaustion plus immediately cooling the victim's body before evacuation to a hospital.
Close attention must be given to the symptoms of heat illness so that the appropriate treatment is given in time to avoid progressively more serious conditions. In many situations, particularly those involving firefighting, road construction, manual labor in warm weather, or simply where there are no ready-made or available sources of shade or cooling, the steps that can be taken to respond to symptoms of heat illness are limited. When there is no area of shade, for example, other means to provide cooling, such as evaporative cooling, are needed.
Prior inventions involving evaporative cooling have not satisfactorily addressed the particular needs for a self-contained, rapidly deployable, mobile evaporative cooling device suitable for firefighting, commercial, or other types of vehicles and suitably designed for relief of heat illness or heat exhaustion symptoms.
One prior invention consists of a portable misting fan. The device consists of a water storage container, a fan, and a mist nozzle. Water stored in the container is dispensed from mist nozzle directly into the fan's airflow stream. This helps atomize the mist into smaller droplets and projects the mist outward covering more area. The system must have a portable electrical means, such as a DC battery pack or electrical AC power source, which requires power cords and, thus, setup time. This design does not lend itself well for fixed mobile application because of the fan and other hardware related to such device and the required time for setting up the system.
Another practice consists of using mist fans or pressure misting systems for outdoor sports (football, soccer, golf, tennis, etc.), sunbathers, lounge areas, over vending machines, and mounting under tents. These water misting apparatuses include several spray nozzles that can be attached to a fixed surface individually or in series. Similar applications may be used at amusement parks to cool people while they are waiting in long lines. This type of technology has been designed for these limited applications (such as outdoor sports) and are not suitably designed for the rapid deployment and mobile heat illness or heat exhaustion recovery applications discussed herein. All of these misting systems require substantial setup or assembly before use.
Other misting systems consist of components such as a water tank, a water pump, and spray nozzle and are available for applications such as golf carts, boats, and baby carriage canopies. These systems are unsatisfactory for mobile heat illness recovery applications because of the low performance components selected, low effective volume or area of mist delivered, the unpleasantly or unsatisfactorily large particle size of the mist dispensed, and assembly or set up required with such systems.